Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from polypropelene (PP material) is a closure suitable for capping, in use, a beverage container, such as, a container for still water or a carbonated drink.
A typical molding system includes inter alia an injection unit, a clamp assembly and a mold assembly. The injection unit can be of a reciprocating screw type or of a two-stage type. Within the reciprocating screw type injection unit, raw material (such as PP, PET or the like) is fed through a hopper, which in turn feeds an inlet end of a plasticizing screw. The plasticizing screw is encapsulated in a barrel, which is heated by barrel heaters. Helical flights of the screw convey the raw material along an operational axis of the screw. Typically, a root diameter of the screw is progressively increased along the operational axis of the screw in a direction away from the inlet end.
As the raw material is being conveyed along the screw, it is sheared between the flights of the screw, the screw root and the inner surface of the barrel. The raw material is also subjected to some heat emitted by the barrel heaters and conducted through the barrel. As the shear level increases in line with the increasing root diameter, the raw material, gradually, turns into substantially homogenous melt. When a desired amount of the melt is accumulated in a space at discharge end of the screw (which is an opposite extreme of the screw vis-à-vis the inlet end), the screw stops its rotation. The screw is then forced forward (in a direction away from the inlet end thereof), forcing the desired amount of the melt into one or more molding cavities. Accordingly, it can be said that the screw performs two functions in the reciprocating type injection unit, namely (i) plasticizing of the raw material into a substantially homogeneous melt and (ii) injecting the substantially homogeneous melt into one or more molding cavities.
U.S. Pat. No. 6,450,797 issued to Joseph on Sep. 17, 2002 teaches a molding apparatus that has a pair of slide inserts which are laterally movable into and out of engagement with the other mold components. The lateral movement of the slide inserts is provided by a slide mechanism having a driving rack, a pair of drive pinions at either end of the driving rack, two pairs of driven racks and a plurality of slides connected to the driven racks. The driven racks of each pair are parallel and spaced from one another, engaging opposite sides of a pinion and thereby being driven in opposite directions by rotation of the pinion. The molding apparatus is more compact than conventional devices having slide inserts, eliminates the use of slide retainers, eliminates obstructions between the mold plates when the plates are separated, and can cycle faster than conventional devices.
U.S. Pat. No. 7,510,677 issued to Miller, et al. on Mar. 31, 2009 discloses an injection molding method and apparatus for ejecting a molded plastic article from a mold. A lifting structure and/or step is provided with a lifting portion which is configured to contact substantially one half of an end of the molded plastic article along a line substantially perpendicular to the lifting direction. Since the molded plastic article is lifted by its end, the article does not have to be solidified at its interior, thus allowing earlier removal of the article from the mold, reducing cycle time. A tapered surface forms an acute angle with respect to the lifting portion to form a tight seal with the mold, preventing leakage. Preferably, the neck ring engages only an outer circumferential portion of the molded plastic article during a majority of a mold opening stroke.
U.S. Pat. No. 4,881,892 issued to Webster, et al. on Nov. 21, 1989 teaches a mold for forming a plastic closure includes a first mold part defining a female cavity and a second mold part defining a male mold cavity surface, with the second mold part including a core having a knock-out pin reciprocated therein and surrounded by a fixed sleeve which cooperate to define a tamper evident band on the cavity for the closure. Vents are provided for venting the lower edge of the cavity during the ejection-molding process. Also, the knock-out pin has a lubricant pocket formed on the peripheral surface thereof.